Table of contents

A description is given of a new class of multicomponent solitons corresponding to stable propagation, in a nonlinear medium, of two or more wave packets which are mutually incoherent, but are matched in respect of the intensity distributions. Such solitons appear as a consequence of cross-modulation self-trapping of zeroth and higher-order modes in a shared nonlinear waveguide formed by these packets.

An investigation was made of the operating characteristics of a linear array of AlGaAs laser diodes indium-soldered to an SiC heat sink. The average output power was 14 W and the efficiency was ∼ 25%. The thermal impedance of the system was 0.05K W^-1. A comparison of the experimental results with heat flow fluctuations showed that, in spite of a thick solder layer, the system was capable of draining heat at an average rate twice that detected experimentally. The discrepancy between the experimental and theoretical results could be explained by structural imperfections of the solder layer, typical of the adopted method for bonding a linear diode array to a heat sink and to electrodes.

Linear and two-dimensional arrays of semiconductor laser diodes were investigated in an external cavity with mirrors of various curvatures. The principle characteristics of the output radiation were determined and feedback optimisation of the investigated system with a mirror (focal length F=1 cm) was carried out. This mirror made lasing possible for 6 diodes in a linear array and for 6 × 5 diodes in a two dimensional array. A mirror with F=20 cm ensured lasing of 14 × 15 diodes. A study was made of the spatial coherence effects in the external cavity. These effects were accompanied by the appearance of an interference pattern in the far-field zone. An experimental confirmation was obtained of theoretical estimates of the dimensions of a linear array in which phase locking is possible.

An experimental investigation was made of the energy and gasdynamic characteristics of a supersonic cw chemical HF laser with a radial-expansion nozzle array of 35 cm × 10 cm dimensions. A nozzle—sonic injector configuration was used for reactant mixing. A specific output energy of 254 J g^-1 and an absolute laser radiation power of 33.5 kW were reached. The distributions of the Mach number, of the static pressure, and of the total pressure behind a plane shock wave in the flowing active medium were measured in wide ranges of the pressure in an atomic-fluorine generator and of secondary fuel (hydrogen) flow rates. The optical quality of the active medium, characterised by the Strehl number St=0.53, was estimated. The advantages and shortcomings of a laser with a proposed nozzle array configuration were identified. Future investigations were outlined.

An analysis is made of the conditions for the generation of superfluorescence pulses in an inverted medium of electron—hole pairs in a semiconductor. It is shown that strong optical amplification in laser semiconductor amplifiers characterised by αL ≫ 1 (α is the small-signal gain and L is the amplifier length) leads to suppression of phase relaxation of the medium during the initial stages of evolution of superfluorescence and to formation of a macroscopic dipole from electron—hole pairs. Cooperative emission of radiation in this system results in generation of a powerful ultrashort pulse of the optical gain, which interacts coherently with the semiconductor medium. It is shown that coherent pulsations of the optical field, observed earlier by the author in Q-switched semiconductor lasers, are the result of superfluorescence and of the coherent interaction between the optical field and the medium.

A unidirectional single-frequency monolithic ring laser with an acousto-optical isolator was proposed and investigated experimentally. Return of the diffracted radiation to the acousto-optical interaction region had a significant influence on the characteristics of the output radiation of such monolithic lasers with a monochromatically pumped end face.

An investigation was made of the generation of powerful stimulated IR radiation in caesium vapour under conditions of an isolated resonance with a transition between the first excited P state and a high S or D level. The main relationships governing the appearance of stimulated IR radiation were established.

An automated system for effective modelling of the kinetic processes occurring in gas lasers was constructed. The main elements of the system are structured physicochemical databases, a generator of kinetic equations, a suite of programs for calculating the equations of gas dynamics in combination with relaxation equations, and program modules for finding the solution satisfying predetermined criteria. A program module was made for ensuring the optimal operating conditions in gasdynamic units in which gas-phase physicochemical processes take place. The example of a gasdynamic laser was used to demonstrate the operation of a module which makes it possible to select a compact group of the main channels that describe satisfactorily this laser. The investigated system can be used successfully to describe kinetic phenomena in an active medium.

An investigation is reported of the influence of quantum noise of amplifying and absorbing media in an active interferometer, excited by an external signal, on its output characteristics. The amplitude and the frequency of the external signal are assumed to be constant. A quantum description of the radiation emitted by an active interferometer is provided by a method involving the use of coherent states. A quantum kinetic equation is derived for the distribution function of the amplitude and phase of the field in an active interferometer and the corresponding diffusion coefficients are found. The variances of fluctuations of the energy of the field and its phase, and also the spectral densities of the fluctuations, are calculated.

A theoretical investigation was made of the dynamics of generation of an optical field in a Fabry—Perot cavity with an active medium and a bleachable filter, considered in the limiting case of an infinitely large aperture. The approximation of a point model was used to describe the cavity, the model equations were solved, and the lasing regimes were classified. More interesting are those regimes in which the field loses its homogeneity and a self-oscillatory modulation of the field appears along the aperture, so that the point model is inapplicable. These regimes were investigated by introducing a self-oscillatory variable into the equations, which makes it possible to dispense with partial derivatives. A theory of nonlinear oscillations can be used to determine the characteristics of wave perturbations (velocity, period, amplitude) near the boundary of a steady-state region; this was done analytically and numerically. Purely harmonic periodic solutions and solutions of an arbitrary type were found. The results showed that an increase in the bifurcation parameter may result in a transition from a periodic wave pattern to a chaotic one, and that this can occur in accordance with various scenarios.

A theoretical investigation is made of the dynamics of a class-B laser emitting the transverse modes TEM₀₀, TEM₁₀, and TEM₀₁. Bifurcation mechanisms of transitions between various lasing regimes are investigated for several intermode intervals and values of the excess above the threshold.

Dynamics of generation of two transverse modes in a class-B laser is investigated theoretically. The bifurcation mechanisms of excitation of steady-state, periodic, and chaotic regimes are studied. It is shown that dynamic transverse structures can either rotate continuously or can oscillate about the optic axis.

The method of direct numerical integration of a system of nonlinear Maxwell's equations was used to investigate the dynamics of formation and interaction of Maxwellian wave solitons of a few femtosecond duration.

A new conservative spatially three-dimensional model is proposed for the interaction of a circularly polarised relativistically strong laser pulse with a cold plasma. Full allowance is made for the wave properties of the radiation and for the potential motion of electrons. A study is reported of the dispersive properties of the problem describing growth of small perturbations against the background of a plane wave. At relativistic intensities the model predicts forward stimulated Raman scattering by plasmons, third-harmonic generation in a narrow forward cone, and backscattering at the fundamental frequency into a wider cone.

An investigation is made of a two-pulse photon echo in a two-level medium with strong inhomogeneous broadening, which is subjected simultaneously to extremely short and quasiresonant pulses. Two variants of the sequence of application of the two pulses are considered and it is shown that the kinetics of an echo signal depends largely on the sequence in which the pulses are applied. Suppression of the photon echo is predicted for both variants when a zero-are extremely short pulse is applied to a medium. A qualitative method for determination of the spatial characteristics of such a combined echo is proposed and used. It is shown that, in the investigated cases, the angular distributions of the echo-signal intensity in an extended medium are not as peaked as in the case of a conventional photon echo.

Equations of two-fluid transient collisionless gas dynamics are used to consider extraction of ions from a low-density laser plasma in connection with laser isotope separation by the AVLIS (atomic vapour laser isotope separation) method and with mass-spectroscopic analysis of the elemental composition of a laser spark. It is shown that during passage of a laser plasma through ion-accelerating grids the ion current is blocked and the plasma is reflected by the grids. A strong field, which breaks up the plasma in the gaps between grids, is insufficient to transport ions across a grid. It is proposed to use a remote electrode under a small electron-extracting potential in order to increase strongly the efficiency of ion extraction in weak fields.

An analysis of the thermoelastic problem is used to formulate the criterion of mechanical damage of a transparent dielectric by laser radiation. The criterion is suitable for calculation of the threshold characteristics of the damage associated with absorbing inclusions and that involving intrinsic mechanisms. It is shown that in the limit of short laser pulses the threshold energy density tends to a constant value for any radiation absorption mechanism. A study is reported of the dependence of the threshold of damage initiated by absorbing inclusions on the pulse duration in a wide range of pulse durations. The theoretical results are compared with the published experimental data.

An analysis is made of the propagation of polarised light in an optical system which consists of a linear polariser and a liquid–crystal layer, of nonuniform thickness, of a liquid crystal in which the director of the molecules is oriented along the tangents to concentric circles. It is shown that there is a one-to-one correspondence between the polarisation of the incident light in the intensity distribution at the output from this optical system.

Detailed morphological investigations were made of craters, formed by laser radiation of various spectral compositions and of different intensities, on the surface of atherosclerotic plaque. It was found that, in the UV spectral range, there was an interval of intensities in which the rate of growth of the crater was maximal and a resection of tissue associated with the formation of shock waves was minimal. Moreover, it was established that, if some of the UV radiation was replaced with visible radiation retaining the same total intensity, the rate of growth of a crater was not affected but mechanical damage of tissue was considerably less.

It is shown that a systematic error, associated with the anisotropic nature of natural fluctuations in a laser, is introduced in measurement of the degree of depolarisation of elliptically polarised laser radiation by a method based on its conversion into linearly polarised radiation.

An investigation is reported of the dependence of the frequency of low-frequency relaxation oscillations of the radiation power of solid-state ring lasers on the nature of the polarisation of the counterpropagating optical waves and on the ring cavity parameters. It is shown that the maximum frequency of antiphase low-frequency oscillations corresponds to the linear collinearly oriented polarisations of the counterpropagating waves. An increase in the ellipticity of the counterpropagating waves reduces the frequency of the antiphase oscillations and this frequency tends to zero for orthogonal circular polarisations of these waves.